The surface-mountable light-emitting diode device of a structure shown in FIG. 5 has hitherto been well known in the art. This surface-mountable light-emitting diode device includes a light-emitting element 41 in the form of a light-emitting diode, a resinous substrate 42 and a transparent resin-molded enclosure 43. The resinous substrate 42 is formed by preparing a double-sided printed substrate having conductive foils deposited respectively on opposite front and rear surfaces thereof, depositing circuit patterns 47a and 47b on the front surface by an etching technique, and forming an anode 46b and a cathode 46a on the rear surface by an etching technique or the like. Subsequently, conductive coating such as an electroless silver plating is deposited on opposite cut side portions of the double-sided printed substrate to form side connecting conductors 48a and 48b so that the circuit pattern 47a and the cathode 46a are electrically connected through the side connecting conductor 48a and the circuit pattern 47b and the anode 46b are electrically connected through the side connecting conductor 48b. 
Thereafter, the light-emitting element 41 having two terminals is mounted on the circuit pattern 47a on the resinous substrate 42 by bonding electrically one of the terminals to the circuit pattern 47a with an electroconductive bonding material 44, and the other terminal is electrically connected to the circuit pattern 47b through a gold wire 45. The resultant assembly is then enclosed with the transparent resin-molded enclosure 43 that is mounted on the front surface of the resinous substrate 42 with the light-emitting element 41 held inside the molded transparent enclosure 43, thereby completing the surface-mountable light-emitting diode device.
However, the above light-emitting diode device utilizing the resinous substrate has the difficulty in dissipating heat generated by the light-emitting element 41 since the metallic electroconductive foil deposited on the resinous substrate 42 to form the circuit patterns 47a and 47b is thin. For this reason, this conventional light-emitting diode device has some problems from a practical perspective in securing a high output capability, an operability at a large current and a high reliability. Also, there is another problem in that since light from the light-emitting element 41 tends to spread in all directions, the rays of light emitted therefrom cannot be utilized efficiently.
On the other hand, the reflection type light-emitting diode device that is manufactured using a lead frame instead of the resinous substrate as discussed above is also known as shown in FIG. 6. This reflection type light-emitting diode device of FIG. 6 is disclosed in, for example, the Japanese Laid-open Patent Publications No. 11-163411 and No. 07-211940.
The reflection type light-emitting diode device shown in FIG. 6 is generally manufactured in the following manner. Specifically, a light-emitting diode element 51 having a pair of terminals is electrically connected at one terminal thereof to one of leads 56a and 56b, which are stamped through a press work by the use of dies or by means of an etching technique, for example, the lead 56a by the use of an electroconductive bonding material 52 and at the other terminal thereof to the lead 56b through a gold wire 53. The assembly including the light-emitting element 51 electrically connected to the leads 56a and 56b is then mounted on a recessed casing 55 having a cavity defined therein, so that the light-emitting element 51 can be oriented downwardly into the cavity of the recessed casing 55, followed by filling of a transparent resinous material 54 into the cavity of the recessed casing 55, with the light-emitting element 51 consequently embedded in the transparent resinous material 54. The recessed casing 55 has a concave interior surface 57 defining the cavity thereof, which is formed as a reflecting surface. The leads 56a and 56b, situated outside the recessed casing 55, are bent downwardly to complete the light-emitting diode device shown in FIG. 7.
In this type of the light-emitting diode device, rays of light emitted from the light-emitting element 51 are, once reflected from the concave reflecting surface 57, radiated to the outside and, therefore, each of the leads 56a and 56b must have a width as small as possible not to obstruct the rays of light traveling from the light-emitting element 51 to the outside of the recessed casing 55. For this reason, in order to achieve high reflection efficiency, each of the leads 56a and 56b must have a width as small as possible as discussed above and the use of the leads 56a and 56b of a small width, however, makes it difficult to dissipate heat, evolved by the light-emitting element 51, to the outside through the leads sufficiently. As a consequence, the thermal resistance of the leads is increased, accompanied by increase of the temperature of the light-emitting element 51, which results in decrease of the lifetime of the light-emitting diode device. In addition, the temperature characteristic of the light-emitting diode device is worsened to such an extent as to decrease the output with passage of time.